1. Field of the Invention
This invention concerns a load isolation system for a tractor which is used primarily for shuttling trailers attached to a fifth wheel boom. The isolation system serves to limit the shock ordinarily transferred from the rear axle to the main frame when the tractor moves over rough or uneven surfaces by including an axle saddle coupled to the main frame by anti-torque links.
2. Description of the Prior Art
Terminal tractors are vehicles which are typically used to shuttle trailers in a port, yard, or other terminal facility. The tractors attach and hold the trailers by a boom which carries a fifth wheel for coupling to the kingpin of the trailer. The boom is pivotally mounted to elevate a trailer carried by the fifth wheel so that the forward support legs are elevated above the ground. This permits the tractor to move the trailer without retracting the support legs which results in much more efficient operation. These tractors are used for only short trips and carry widely varying loads, and in order to reduce cost, are typically provided without dampening suspension systems, but instead the axle and fifth wheel are rigidly mounted to the frame. As a consequence, the cab and driver, as well as the engine, frame, and other components are subjected to continuous stress and strain as the tractor drives over the surface.
One effort to overcome these problems is shown in U.S. Pat. No. 5,020,820 to Renner, et al. This patent shows a suspension system for a tractor-trailer combination which uses an A type sub-frame connected to the main frame by a universally pivoting coupling at the front apex of the A-frame. The rear of the A-frame is coupled to the rear axle with the fifth wheel load being applied to the A-frame by the lift cylinders. Pneumatic cushions and shock absorbers are interposed between the A-frame and the main frame to cushion the tractor. While this tractor suspension presents certain advantages, certain problems have also been presented, such as overloading of the pneumatic cushions as a result of an overload on the fifth wheel, causing the cushions to burst. These problems include the necessity for providing plural suspension means such as pneumatic cushions and shock absorbers between the subframe and the main frame, maintenance difficulties in connection with the pneumatic cushions, clearance below the main frame of the tractor which may be limited by the forwardly extending A-frame, and stress on the driveshaft occasioned by the geometry of the A-frame. Additionally, the suspension system of the prior art requires an additional hydraulic system for controlling the amount of suspension for the load, and failed to provide any suspension effect when the fifth wheel boom was in a "down" position.
As a consequence, there has developed a real need for a rugged, reliable, load isolation system for a tractor which can avoid the aforementioned problems.